System and method for managing battery discharge during critical peak pricing intervals

Abstract

A system and method are provided for managing battery discharge during critical peak pricing (CPP) intervals. The method provides an alternating current (AC) client with a fluctuating AC grid demand, and a direct current (DC)-to-AC inverter having an input connected to a battery and selectable inversion power output levels connected to the AC client. In response to receiving a CPP warning for a first time interval, a present battery capacity state of charge (SoC) is determined. Also determined is a target peak demand for the AC client over a second time interval that includes the first time interval. The target peak demand defines a desired maximum threshold AC grid demand. In response to determining the present battery capacity SoC and the target peak demand, excess battery capacity is determined, and the excess battery capacity is used to supply auxiliary energy to the AC client during the CPP first time interval.

We claim: 
     
       1. A method for managing battery discharge during critical peak pricing (CPP) intervals, the method comprising:
 providing an alternating current (AC) client with a fluctuating AC grid demand, and a direct current (DC)-to-AC inverter having an input connected to a battery and selectable inversion power output levels connected to the AC client; 
 selectively supplying auxiliary power from the DC-to-AC inverter to at least partially satisfy the AC grid demand; 
 receiving a CPP warning for a first time interval; 
 determining a present battery capacity state of charge (SoC); 
 determining a target peak demand for the AC client over a second time interval that begins at a start of the first time interval, where a target peak demand defines a desired maximum threshold AC grid demand; 
 in response to determining the present battery capacity SoC and the target peak demand, determining excess battery capacity; and, 
 using the excess battery capacity to supply auxiliary energy to the AC client during the CPP first time interval. 
 
     
     
       2. The method of  claim 1  wherein determining the target peak demand includes estimating a lowest peak demand limit that is possible over a remaining second time interval based upon the present battery capacity SoC. 
     
     
       3. The method of  claim 2  wherein determining the target peak demand includes:
 estimating the lowest peak demand limit based upon a consideration of current, predictive, and historical data selected from a group consisting of power usage and weather forecasts; 
 comparing the estimated lowest peak demand limit to a highest peak demand recorded in a present billing period; and, 
 selecting the peak demand with a larger peak limit value as the target peak demand. 
 
     
     
       4. The method of  claim 1  wherein determining excess battery capacity includes:
 determining the battery capacity required to satisfy the target peak demand for a remaining portion of the second time interval, to find a target capacity; 
 multiplying a full battery capacity by the present battery capacity SoC to determine a present battery capacity; and, 
 subtracting the target capacity from the present battery capacity to find the excess battery capacity. 
 
     
     
       5. The method of  claim 4  wherein using the excess battery capacity to supply auxiliary energy during the CPP first time interval includes computing a battery rate of discharge during the CPP first time interval, as follows:
 in the CPP first time interval, subtracting a third time interval value associated with the time the DC-to-AC inverter supplies a maximum battery rate of discharge to maintain the target peak demand from the time remaining in the CPP first time interval, to find a fourth time interval value; and, 
 dividing the excess battery capacity by the fourth time interval value to find a CPP discharge power. 
 
     
     
       6. The method of  claim 5  wherein using the excess battery capacity to supply auxiliary energy during the CPP first time interval additionally includes discharging the battery at a rate of:
 the CPP discharge power, when the AC grid demand is less than or equal to the target peak demand; and, 
 the maximum battery rate of discharge, when the AC grid demand is greater than the target peak demand. 
 
     
     
       7. The method of  claim 1  wherein determining excess battery capacity includes:
 determining the battery capacity required to satisfy the target peak demand for a remaining portion of the second time interval subsequent to the end of first time interval, to find a remainder capacity; and, 
 multiplying a full battery capacity by the present capacity SoC to determine a present battery capacity; 
 subtracting the remainder capacity from the present battery capacity to find the excess capacity. 
 
     
     
       8. The method of  claim 7  wherein using the excess battery capacity to supply auxiliary energy during the CPP first time interval includes discharging at a maximum battery rate of discharge under conditions selected from a group consisting of:
 when the excess capacity expires by the end of the first time interval, or after; 
 when the excess capacity is determined to expire before the end of the first time interval, and the AC grid demand is greater than the target peak demand; and, 
 discharging at a zero rate of battery discharge when the excess capacity is determined to expire before the end of the first time interval, and the AC grid demand is less than or equal to the target peak demand. 
 
     
     
       9. The method of  claim 8  further comprising;
 in response to discharging at the maximum battery rate of discharge, receiving a power credit when the power discharged from the battery exceeds the AC grid demand. 
 
     
     
       10. A system for managing battery discharge during critical peak pricing (CPP) intervals, the system comprising:
 a battery to supply auxiliary power; 
 a direct current-to-alternating current (DC-to-AC) inverter having an input connected to a battery and selectable inversion power output levels connected to an AC client to supply auxiliary power; 
 a measurement module having an interface to receive a CPP warning for a first interval of time, an interface connected to the battery to determine a present battery capacity state of charge (SoC), and an interface connected to the AC client to determine a target peak demand for the AC client over a second time interval that begins at a start of the first time interval, where a target peak demand defines a desired maximum threshold AC grid demand; and, 
 a controller having an interface to receive an excess battery capacity determination from the measurement module, responsive to the target peak demand and the present battery capacity SoC, and an interface connected to the DC-to-AC inverter to command the supply of the determined excess battery capacity during the CPP first time interval. 
 
     
     
       11. The system of  claim 10  wherein the measurement module determines the target peak demand by estimating a lowest peak demand limit that is possible over a remaining second time interval based upon the present battery capacity SoC. 
     
     
       12. The system of  claim 11  wherein the measurement module estimates the lowest peak demand limit based upon a consideration of current, predictive, and historical data selected from a group consisting of power usage and weather forecasts, compares the estimated lowest peak demand limit to a highest peak demand recorded in a present billing period, and then selects the peak demand with a larger peak limit value as the target peak demand. 
     
     
       13. The system of  claim 10  wherein the measurement module determines the battery capacity required to satisfy the target peak demand for a remaining portion of the second time interval, to find a target capacity, multiplies a full battery capacity by the present battery capacity SoC to determine a present battery capacity, and then subtracts the target capacity from the present battery capacity to find the excess battery capacity. 
     
     
       14. The system of  claim 13  wherein the measurement module computes a battery rate of discharge during the CPP first time interval, as follows:
 in the CPP first time interval, subtracting a third time interval value associated with the time the DC-to-AC inverter supplies a maximum battery rate of discharge to maintain the target peak demand, from the time remaining in the CPP first time interval, to find a fourth time interval value; and, 
 dividing the excess battery capacity by the fourth time interval value to find a CPP discharge power. 
 
     
     
       15. The system of  claim 14  wherein the measurement module determines the excess battery capacity as the CPP discharge power when the AC grid demand is less than or equal to the target peak demand, and the maximum battery rate of discharge when the AC grid demand is greater than the target peak demand. 
     
     
       16. The system of  claim 10  wherein the measurement module determines the battery capacity required to satisfy the target peak demand for a remaining portion of the second time interval subsequent to the end of the first time interval, to find a remainder capacity, multiplies a full battery capacity by the present battery capacity SoC to determine a present battery capacity, and then subtracts the remainder capacity from the present battery capacity to find the excess capacity. 
     
     
       17. The system of  claim 16  wherein the memory module determines the maximum battery rate of discharge in a condition selected from a group consisting of when the excess capacity expires by the end of the first time interval, or after, and when the excess capacity is determined to expire before the end of the first time interval and the AC grid demand is greater than the target peak demand; and,
 wherein the memory module determines a zero rate of battery discharge when the excess capacity is determined to expire before the end of the first time interval, and the AC grid demand is less than or equal to the target peak demand. 
 
     
     
       18. The system of  claim 17  wherein the controller commands the DC-to-AC controller to discharge at the maximum battery rate of discharge; and,
 wherein the AC client receives a power credit when the power discharged by the DC-to-AC inverter to the AC client exceeds the AC grid demand.